CONFERVOIDE.E. 



[ 159 ] 



CONFERVOIDE.E. 



one of the favourite and most instructive 

 fields of microscopic research. As yet, how- 

 ever, the minute history of development is 

 wanting in a very large number, while the 

 facts already disclosed are so varied, that it 

 becomes a matter of difficulty to draw up a 

 sketch of their characteristics in a brief space. 

 The classification of the tribes standing on 

 the boundaries between the Coufervoids and 

 the Fucoids is in an unsettled condition, and 

 the real nature of the fructification of the 

 Lemanieae and Batrachospermeae may be 

 considered open to doubt. The detection by 

 Thuret of zoospores in so many of the true 

 Fucoids, takes away the ground on which 

 these two families have been included in that 

 order; and at present we prefer to leave them 

 among the Confervoids, where, however, it 

 is true they stand in rather an isolated posi- 

 tion ; but the forms of reproduction are 

 so varied here, that this seems of the less 

 consequence. 



Among the Palmellaceae we find some of 

 the simplest forms of vegetable life, where 

 the organization is reduced to the condition 

 of a single microscopic membranous vesicle, 

 enclosing nitrogenous contents, ordinarily 

 tinged with chlorophyll, and containing 

 starch. Such we have in Chlorococcum vul- 

 gare, which forms the dryish green powder 

 upon palings, trunks of trees, &c. This 

 form appears to multiply only by the subdi- 

 visions of its cells into two or four new ones, 

 which separate and repeat the process. It 

 is a somewhat doubtful plant, but if a di- 

 stinct organism, it is the lowest of the Algae. 

 Advancing a step, we come to a number of 

 genera not yet well defined, in which the mem- 

 branes of the parent-cells soften into a kind 

 of gelatine, during the process of subdivision, 

 and hold the new cells together in groups of 

 definite or indefinite form ; among these are 

 Palmella, Glceocapsa, and others of like na- 

 ture, in which at present no zoospores have 

 been discovered. In Coccochloris a process 

 of conjugation occurs. Side by side with 

 Chlorococcum,^ regards organization, stands 

 the genus Protococcus, in which, in addition 

 to the vegetative growth by subdivision 

 going on in damp air (the cells being held 

 together more or less firmly into a gelatinous 

 crust), the contents of the individual cells 

 are set free by solution of the membranes 

 when placed in water, and emerge as ciliated 

 zoospores, endowed with active motion. 

 These genera also exhibit a resting form, 

 characterized by the increased thickness of 

 the membrane of the cell, and a change of 



the green contents into a brownish, reddish, 

 or even crimson colour. 



The Ulvaceas are not widely separated 

 from the Palmellacese, but the conjunc- 

 tion of the cells into a definite membrane 

 indicates a higher organization. In other 

 respects, however, they hardly differ more 

 from some of the more perfect genera of 

 Palmellaceae than those do from Protococcus ; 

 and therefore, although more conspicuous 

 and extensively developed than the Nosto- 

 chaceae and Desmidiaceae, it seems natural to 

 place the Ulvaceae near the Palmellaceae, espe- 

 cially as the reproduction by cell-division and 

 by zoospores is analogous in all respects to 

 what is seen in Protococcus, of which they 

 would appear to be the permanently aquatic 

 representatives. Prasiola and Schizogonium, 

 however, differ from the other Ulvaceae in the 

 absence of zoospores, the contents (homo- 

 geneous, not granular) of the cells being 

 discharged as motionless spore-like bodies, 

 from which new fronds grow up. Some 

 authors separate these genera, but we are 

 hardly in a position to determine the exact 

 place of these plants at present. 



The Nostochaceae exhibit but a slight 

 advance in the organization over the Palmel- 

 laceae. They are composed of linear series of 

 cells, mostly inflated, so as to give the fila- 

 ments a beaded appearance ; the linear series 

 increase in length by transverse division, 

 and also in some stages subdivide laterally ; 

 larger globular (spermatic) cells occur at 

 intervals in the lines, with others devoid of en- 

 dochrome (vesicular cells, Thwaites). During 

 the increase, the older external membranes 

 soften into a gelatinous coat. In Nostoc, where 

 the filaments accumulate in large quan- 

 tity, they lie elegantly curled and entwined 

 in masses of this jelly, which exhibit a more 

 or less definite, lobed, external form, appear- 

 ing to the naked eye as gelatinous crusts or 

 globular masses, as they lie upon damp 

 ground or among mosses. No other mode 

 of increase but by subdivision has yet been 

 observed here, but it is not improbable 

 that some different kind may be detected 

 hereafter. 



Nearly allied to Protococcus stand a 

 family which until recently have been re- 

 garded by most authors as animals, namely 

 the Volvocineae, which consist essentially of 

 groups of organisms identical with the cili- 

 ated zoospores, held together in a definite 

 form by a common membranous envelope, 

 through which the cilia penetrate, so that 

 the entire full-grown plant moves freely in 



